Can Cast Aluminum Be Heat Treated

Imagine designing a critical component only to find that its strength and durability cannot fully meet the required performance standards.

This is a common challenge in the manufacturing process, especially when using aluminum alloys in demanding applications.

To address this issue, engineers typically consider heat treatment as a solution. However, can all cast aluminum alloys be effectively heat treated, and which processes produce the best results?

Casting methods such as low-pressure die casting, sand casting, and squeeze casting are usually compatible with heat treatment and can improve mechanical properties. In contrast, processes such as high-pressure die casting and permanent mold casting (steel mold casting) are usually not suitable due to porosity and structural limitations.

It is important to choose a casting process that matches the heat treatment to improve the strength, durability, and overall performance of aluminum castings.

In this article, we will study which casting processes are compatible with heat treatment, explore commonly used heat treatment methods, and emphasize the advantages that heat treatments bring to aluminum castings.

Casting Processes Suitable for Heat

The following outlines the main casting methods highly compatible with heat treatment:

Low-Pressure Die Casting

In low-pressure die casting, molten aluminum is injected into the mold under low pressure to minimize air pores and form a dense structure that responds well to heat treatment.

This method is very suitable for producing castings that require both strength and dimensional accuracy and can improve their properties after heat treatment.

Sand Casting

Sand casting is a type of gravity casting that involves pouring molten aluminum into a sand mold.

Commonly used aluminum alloys such as A356 come with good heat treatment reactions, which can improve hardness and strength.

The flexibility of design combined with the alloy’s responsiveness to heat treatment makes sand casting suitable for manufacturing sturdy aluminum components.

Squeeze Casting

Squeeze casting applies high pressure during the solidification process, combining the advantages of casting and forging.

This process eliminates shrinkage, reduces porosity, and produces a dense structure with refined grains.

At CEX, our advanced squeeze casting technology achieves extremely low porosity, maximizing the effectiveness of heat treatment and giving the parts excellent strength and durability.

Casting Processes Not Suitable for Heat Treatment

The following two common casting processes usually come with weak compatibility with heat treatment due to issues such as porosity and structural limitations:

High-Pressure Die Casting

High-pressure die casting refers to injecting molten aluminum into a mold at extremely high pressure to rapidly solidify it.

However, this process traps air in the metal, creating pores that limit compatibility with heat treatment.

Gas expansion during heat treatment can cause warping or cracking, so high-strength parts are generally avoided using a high-pressure die casting process.

Permanent Mold Casting

Permanent mold casting uses reusable steel molds to produce parts with smooth surfaces and consistent dimensions.

However, parts manufactured by this method still have some porosity and alloy limitations, which affect the heat treatment effect.

Common Heat Treatment Processes

For cast aluminum, the most widely used heat treatment processes are T4, T5, and T6, each of which can provide specific enhancements to the material’s properties.

The following three tables show the parameters of different heat treatment methods and the achievable mechanical properties of aluminum castings with different casting processes after heat treatment.

Taking the most commonly used A356 aluminum as an example, demonstrate the properties that can be achieved under sand casting and CEX’s squeeze casting after heat treatment:

Table 1: Parameters of T4, T5, T6 Heat Treatment

Heat Treatment Method	Solid Solution Treatment Temperature	Duration of Solid Solution Treatment	Aging Type	Aging Temperature	Duration of Aging	Applicable Characteristics
T4	about 500°C	1~2 hours	natural aging	room temperature	days to weeks (depending on specific materials)	ideal for parts requiring high plasticity and toughness, suitable for lightweight structures and non-critical applications like decorative components
T5	–	–	artificial aging	150°C~200°C	2~5 hours	suitable for medium-strength applications, offers good strength and workability, commonly used in automotive parts and household items
T6	约500°C	1~2 hours	artificial aging	160°C~180°C	4~8 hours	designed for high-strength and reliability needs, ideal for aerospace and heavy machinery, ensuring performance under extreme conditions

Table 2: Mechanical Properties of A356 Aluminum Sand Castings After T4, T5, T6 Heat Treatment

Heat Treatment Method	Tensile strength (MPa)	Yield Strength (MPa)	Elongation (%)	Hardness (Hb)
T4	180 – 240	110 – 150	8 – 12	60 – 80
T5	210 – 250	150 – 190	5 – 10	70 – 90
T6	260 – 300	200 – 240	3 – 10	90 – 105

Table 3: Mechanical Properties of CEX’s A356 Aluminum Squeeze Castings After T5 and T6 Heat Treatment

Which Heat Treatment Fits Each Casting Process?

Each casting process produces a different alloy structure, which affects its compatibility with specific heat treatments.

Choosing the optimal heat treatment for each casting process can maximize the performance and service life of castings:

Aluminum Alloy Casting Process	Suitable Heat Treatment Method
Low-Pressure Die Casting	T5, T6
Sand Casting	T4, T6
Squeeze Casting	T6
High-Pressure Die Casting	not recommend
Permanent Mold Casting (Steel Mold Casting)	not recommend

The Advantages of Heat Treatment

Heat treatment can significantly improve the performance of cast aluminum. Let’s take a comprehensive look at the main advantages of heat treatment:

Increased Strength and Durability

Heat treatment, especially T6 heat treatment, greatly improves the strength, hardness, and fatigue resistance of cast aluminum, making it an ideal material for high-stress components.

The improvement of durability also reduces the need for maintenance and replacement, which is very advantageous in harsh environments that require long-term reliability.

Improved Machinability

Aluminum castings that have undergone heat treatment typically come with higher machining efficiency and less deformation and wear of cutting tools.

This improvement can produce complex, high-tolerance components more accurately.

Enhanced Corrosion Resistance

Heat treatment can improve corrosion resistance, making it suitable for aluminum castings exposed to moisture, chemicals, or salt environments.

This additional protection extends the service life of aluminum components under harsh conditions, helping to maintain their appearance and functionality over time.

CEX Casting Case Study

At CEX Casting, we combine heat treatment with our advanced squeeze casting process to produce aluminum castings with excellent mechanical properties and durability for our customers. Below is a typical example:

A leading electric motorcycle manufacturer approached us to address significant issues with their hydraulic brake part.

This part was previously produced via high-pressure die casting and came with issues of porosity and oil leakage, raising concerns about long-term reliability and user safety.

After careful evaluation, we recommend using A356 aluminum produced via squeeze casting followed by T6 heat treatment. Below is detailed info on the part we produced: